Last night's televised debate on Channel 4 between the would-be next chancellors of the exchequer — Ed Balls excepted — was a victory for serious televised political argument. It did all the participants — Alistair Darling, George Osborne and Vince Cable — considerable credit. All of them had important points to make. None of them was rattled. All of them were competent. They argued — and there was much to argue about. But it was civil stuff. In many respects the debate was an implicit reprimand to the clunkier and more confrontational culture of parliamentary debating. It was a vindication of the decision to hold televised match-ups between the party leaders in a few weeks time. Already it seems incredible that Britain has waited so long to hold such debates.

The single most striking thing about the chancellors' debate, however, was that it was a genuine three-way contest. Parliamentary debates maintain the pretence that we still have only two parties. But that's not true. We have three — and more. The presence in the debate of the Liberal Democrat Vince Cable changed the dynamic from the old Labour versus Conservative slanging match to something more nuanced, more problem-orientated and more truthful. It was striking too that Mr Cable and Mr Darling banded together more often against Mr Osborne than Mr Cable and Mr Osborne did against Mr Darling. There is a reminder there of something important about British politics generally — that this is not overall a centre-right country. In yesterday's debate the centre of gravity was on the centre-left. That is an accurate reflection of the country too, even now.

As the man in charge, Mr Darling ought perhaps to have been the man in the dock. In fact, he was not; Mr Osborne got more of a grilling. That reflects well on Mr Darling, who has steadily gained trust and respect from his handling of the hardest set of tasks that have faced any chancellor in recent times. He made sure that we were reminded of that fact — and it was noticeable that the name Gordon Brown scarcely crossed his or anyone else's lips all evening. Mr Darling's virtues, his calm, his strategic sense and his truthfulness were all on parade last night. He may not have won many converts but he surely lost none either. His performance will probably have confirmed those who are contemplating a Labour vote that they will stick with their choice.

The same is broadly true of Mr Osborne and those who are planning a vote for the Tories too, for all that the others roughed him up a few times. Mr Osborne had two selling points last night. First, that his calm under fire probably did his callow and frivolous public image some good and, second, that he had something new to say in the shape of yesterday's well-trailed offer that the Tories will cancel much of Labour's planned 2011 national insurance contributions increase. The coming weeks will be a big test of whether this country is still susceptible to such a 1980s-style individualist pitch or whether we are a more chastened and circumspect electorate — as we ought to be.

It was, though, Mr Cable's night. The Liberal Democrat had a good story to tell about his grasp of the economic crisis. "I got it right" was his trump card, and he played it often. He had other cards in his hand, however, not least his direct answer about the programmes he would cut and the trenchancy of his answers on the banks and on tax reform. He was also the one participant who clearly argued the case for a new kind of economy. In some ways Mr Cable had more to lose last night than his rivals. Having gained such a strong reputation in the crisis he could have lost credibility by seeming irrelevant to the contest between the bigger parties. In fact he more than held his own. On the first important platform of the election Mr Cable established that there are at least three choices in this contest, not just two. First round to the Lib Dems. Now bring on the main event.